An organic EL element is promising for next-generation displays and next-generation lighting devices, and has been actively researched and developed in the country and in foreign countries. Various metal complexes have been reported as a luminescent material for an organic EL element with the view of enhancing efficiency, improving color purity, and extending the life span. (See Patent Documents 1 and 2, for example.)
Meanwhile, Non-Patent Documents 1, 3 and 4 disclose binuclear metal complexes, and methods of producing the complexes, but do not disclose any properties as a material for an organic EL element. Non-Patent Document 2 reports the synthesis of binuclear iridium complexes, and the examination of binuclear iridium complexes as a luminescent material for an organic EL element. Patent Documents 3 and 4 disclose binuclear metal complexes, and methods of producing the complexes, but do not disclose the complexes of the present invention such as a complex containing a biimidazole as a bridging ligand, for example.